The present invention relates to an insert for chip removing machining. The insert comprises a mainly polygonal body of hard, wear resistant material which has an upper face and a lower face arranged in separate, mainly parallel planes and a plurality of side faces connecting said faces. At least one chip breaker is assymmetrically arranged in at least one of the upper or lower faces and at least one nose portion provided with a cutting edge. The chip breaker consists of an outer part and an inner part, said outer part forming a cutting edge at the intersection of a first side face. The end of the inner part in the vicinity of the nose portion deviates from the main direction of the inner part such that the distance between the end and the connected cutting edge or its extension line in a plane, parallel with the lower face, increases with diminishing distance to a second side face. The cutting edge, the nose portion and the edge of the nose portion are arranged at a distance from the associated upper or lower face.
Hitherto known inserts for chip removing machining have chip breakers at the rake face, which have an extension along the cutting edge in direction from one cutting corner towards an adjacent cutting corner. One end of the chip breaker starts off in a side face of the insert such that the minimum point in the side face will lie below the highest point of the associated nose portion. Thus, the cutting corner will achieve a neutral or negative cutting geometry around the minimum point of the chip breaker in the side face, said cutting geometry transferring into positive the closer to the longitudinal cutting edge the rake angle is measured. The negative cutting geometry results in that the cutting forces acting upon the work piece and the insert become larger and therefore the insert risks breaking. Furthermore, the inner part of the chip breaker, as a whole, has a straight extension which means that the insert during small feed rates and cutting depths, when mainly only the nose portion works, does not form the chips in a satisfactory manner. The chips cut in that manner by the conventional insert achieve a large radius of curvature and a steep pitch and therefore they have a tendency to coil around the work piece and insert and therefore risk to damage these especially during turning of tough work material having a low carbon content.
The invention is intended to provide an insert having a shape avoiding the above-mentioned drawbacks.